Effects of low-frequency high-intensity interval training on improving obesity and depression

Abstract

The prescription of aerobic exercise intervention for improving metabolic and mental health was conventionally determined at moderate intensity conducted three times weekly, but little is known about the training effects of aerobic exercise at a lower frequency and at vigorous intensity. This thesis aimed to compare the training effects of aerobic exercise at different exercising frequencies and intensities in adults with overweight, obesity or depressive symptoms. This thesis contains four randomized controlled trials. The first randomized controlled trial (Chapter 2) showed that eight weeks of low-frequency high-intensity interval training (HIIT) could improve body composition and aerobic fitness in overweight and obese young adults. The second randomized controlled trial (Chapters 3 and 4) further investigated the effectiveness of one-year low-frequency HIIT on body adiposity and liver fat among adults with central obesity. The results of Chapters 2 and 4 showed that low-frequency HIIT reduced body adiposity and improved cardiorespiratory fitness. Additionally, the findings in Chapter 4 showed that low-frequency HIIT could alleviate the level of depression among adults with central obesity. The third pilot randomized controlled trial (Chapter 5) compared the effects of HIIT and moderate-intensity continuous training at low exercise frequency (i.e., one session weekly) on body adiposity among adults with central obesity. The fourth randomized controlled trial (Chapter 6) examined the effects of different aerobic exercise frequencies and intensities on reducing depressive symptoms in older adults with chronic insomnia. The results demonstrated that the impact of walking training on reducing depressive symptoms appeared to be dependent on exercise frequency. The findings suggested that three walking sessions per week at either moderate or vigorous intensity, as defined by the World Health Organization (WHO), effectively alleviates depressive symptoms and improve sleep in older adults. In conclusion, these findings revealed that HIIT performed once weekly was sufficient to induce beneficial adaptation by reducing body adiposity, liver fat, body weight, and waist circumference in adults with overweight or obesity. We also found that once weekly HIIT could reduce depression among adults with central obesity, but once weekly walking exercise with moderate or vigorous-intensity could not alleviate depressive symptoms among older adults with insomnia. The low-frequency exercise approach enhances the practical suitability of aerobic training through reducing the time commitment for physically inactive individuals. This thesis provided evidence that low-frequency HIIT is an effective exercise option to induce improvement in body fatness, liver fat, waist circumference, cardiorespiratory fitness, and depression.